Train order enforcement system



Oct. 23, 1962 J. w. PORTER TRAIN ORDER ENFORCEMENT SYSTEM 5 Sheets-Sheet 1 Filed Sept. 30, 1959 BY JWPORTER mE/Z HIS ATTORNEY Oct. 23, 1962 J. w. PORTER TRAIN ORDER ENFORCEMENT SYSTEM Filed Sept. 30, 1959 3 Sheets-Sheet 2 Di CD 4 U3 CD (1i-. i F I O I J o: C0 D:

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vs/.PORTER HIS ATTORNEY Oct. 23, 1962 J. w. PORTER TRAIN ORDER ENFORCEMENT sYsTEM 3 Sheets-Sheet 3 Filed `Scepl'l 30 1959 Tzmm ma A 3&5@ 23E mon.

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JWPORTER RWM HIS ATTORNEY United States Patent r l 3,060,311 TRAIN ORDER ENFORCEMENT SYSTEM John W. Porter, Rochester, N.Y., assignor to General Railway Signal Company, Rochester, N.Y. Filed Sept. 30, 1959, Ser. No. 843,553 11 Claims. (Cl. 246-4) This invention relates to systems for dispatching trains on railroads, and more particularly pertains to a system for enforcing train orders issued by a dispatcher for train movements on a single track railroad having passing sidings.

In the operation of railroads where the control of the trains is effected through dispatching orders of the telegraph or telephone type, it is necessary on a single track railroad to issue a particular kind of an order which must be strictly adhered to especially in connection with the meeting of trains of opposing directions at passing sidings. This is true regardless of whether the railroad is one without signaling or one which is provided with absolute permissive block signaling such as shown in the prior U.S. Patent No. 2,352,986, dated July 4, 1944. In the lirst instance the trainmen operating the trains must remember their orders for meeting or passing at a particular passing siding. In the second instance, when a block signaling system of the absolute permissive block type is employed, there are situations when a train might have a clear indication at a meeting point because the train which it is meeting is too far distant to provide an indication of an opposing train on the signaling system.

For the above reasons, it is desirable to provide some form of supervisory control Which will enforce train orders in connection with train meets and passes.

Generally speaking, and without attempting to exactly define the scope of the present invention, it is proposed that each train be equipped with some form of train stop or train control with appropriate wayside apparatus at the entrance to passing sidings for causing the actuation of the train control in a way to stop a train unless said wayside apparatus is acted upon by some remote centrally controlled means for the passage of such train. Although the remote control is of the selector type momentarily effective, the wayside apparatus is conditioned to clear a train after such control is once received only until a train passes such wayside apparatus at which time it is again restored to its normal condition in which it would cause the stopping of a passing train. In this way, any failure on the part of the remote control apparatus for subsequently clearing the wayside apparatus does not result in the erroneous passage of a train. This renders the entire system operative upon the side of safety.

It is proposed that the system of the present invention be embodied in simple apparatus and so organized as to be effective for all types of railroads Whether or not they are provided with a conventional wayside signal.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompany in drawings, and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawings, in which like reference characters designate corresponding parts throughont the several views, and in which:

FIG. l illustrates in a diagrammatic manner the system of the present invention applied to a stretch of single track of unsignaled territory employing a separate remotely controlled selector for each end of each passing siding;

FIG. 1A illustrates diagrammatically one suitable train carried equipment which may be used in the present invention; and

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of the present invention applied to a stretch of single track railroad employing wayside signaling of the absolute permissive block signaling type with a separate remotely controlled selector for each end of the passing siding.

For the purpose of simplifying the illustration facilitating the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawing having been made more with the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specilic construction and arrangement of parts that would be employed in practice. Thus, the various relays and other electrical equipment are illustrated in the conventional manner, and symbols are used to indicate connections to the terminals of batteries, or other sources of electric current instead of showing all the wiring connections to these terminals.

The symbols and are employed to indicate positive and negative terminals respectively of suitable batteries or other sources of direct current; and the circuits with which these symbols are used, always have current owing in the same direction.

Referring to FIG. 1, a stretch of single track TK is provided with a passing siding PS. It should, of course, be understood that the entire stretch of railroad may have other similar passing sidings at which similar apparatus is installed. At a central office 3, suitable control apparatus is located to establish selective communication between it and all of the passing sidings over a pair of line wires 1 and 2. These line wires 1 and 2 are contemplated in accordance with the present invention as being a pair of line wires used for telephones and to which a suitable telephone type selector is attached at the central otlice and at each of the passing sidings for ringing or giving other suitable signals for the telephones at such locations. One suitable telephone selector system of this type is described in the book entitled Railway Train Dispatching Telephone Systems, published by the Western Electric Co., of New York City, New York, as their Bulletin No. 672A.

Such a telephone selector system includes in the central otice a control panel upon which diierent call codes may be set up and then rendered effective to be transmitted over the pair of line wires 1 and 2 to the various stations at the passing sidings. At each station, a suitable remote control telephone selector 4 is connected across the line wires and these selectors are arranged to close contacts 15 or 19 (for station A) only when their station is called by particular codes applied to the line. These selectors can be arranged to selectively close any one of four different circuits so that any one of four local signal circuits can be closed -by the same selector when an appropriate code is received.

In accordance with the present invention, it is only necessary for two such contacts to be employed for the train control, so that the other two contacts may be employed for selectively calling (by establishing a signal) a trainman to a telephone connected to the line wires 1 and 2 but not specifically shown.

With more particular reference to station A, the reception of a clear control code momentarily closes contact l15, while the reception of a stop control code momentarily closes contact 19. Closure of contact .15 eiects the pick up of storage relay DS, but closure of contact 19 eects the release of its stick circuit. The relay DS in turn controls a wayside inductor or track element -T for the entrance to the passing siding. Such inductor T is adapted to cooperate with a suitable train control system of the train stop type. On each train FIG. 2 illustrates in adiagrammatic manner the system is a suitable receiver or locomotive element L which cooperates with the track element T to stop the train in the event that the winding `12 on the track element T is not short-circuited under `the control of its associated relay DS.

Also, associated with each track element or inductor T is a relay IN which is actuated by the current induced in the winding 12 upon the passage of a locomotive carried element L. Such response of the relay IN causes the associated relay DS to be released.

This train control system may be of any suitable type but for convenience and deniteness in the illustration it is assumed to be an intermittent inductive type of train control such as disclosed in the U.S. Patent to C. S. Bushnell, No. 1,686,434 granted October 2, 192.8. The train carried apparatus as disclosed in FIG. 2 of such patent has been shown for convenience in FIG. 1A, in which the apparatus has been given the same letter reference characters as in the patent; but, for the sake of simplicity the numerical reference characters have been omitted. Also, the same battery symbols (B) and (C) have been employed. In this connection, it should be understood that (B) represents the positive terminal of a suitable source and (C) represents the negative Iterminal of such source.

Although reference may be made to the Patent No. 1,686,434 for a detailed explanation of the operation of FIG. 1A, such operation will now be briefly summarized with reference to FIG. 1A for the purpose of an understanding of the present invention.

Under normal conditions, the relays CR, RR and BR are energized. Energy is also normally supplied to the electro-pneumatic valve EPV which maintains the brakes removed insofar as the automatic control thereof is concerned. The normal energization of the relay BR also includes the primary winding P of the train carried receiver L. This produces a normal magnetic flux in the laminated soft iron core of the receiver L.

The steady magnetic flux in the receiver L does not produce any inductive current in the secondary winding S which is included in series in the energizing circuit for the relay CR. However, when the receiver L passes over a wayside track element or inductor T which has its winding 12 open circuited, the ilux in the receiver L rapidly increases because the reluctance of the open air leakage path has been greatly reduced by the track inductor T. Such temporary increase of the flux in the receiver L as the train moves along causes a current to be induced in the secondary winding S which is in opposition to the normal current ow in the relay CR. Such reduction in the current flow through the relay CR causes it to release which in turn is repeated by the relays RR and BR to in turn deenergize the electro-pneumatic valve EPV and automatically apply the brakes. If this occurs, normal conditions can be restored only by the stopping of the train and the actuation of the push button PB which is usually located in such a position as to be manually operative only if the train is actually stopped. Such actuation restores the normal energized condition of the relays CR, RR and BR which in turn allows the electropneumatic valve EPV to become normally energized upon the release of the push button PB.

On the other hand, if the engineman is alert when passing the wayside inductor T, then he can actuate the acknowledgment button ACK which will then maintain the brake control relay BR energized although the relays CR and RR are momentarily released and then restored. Such operation of the lever ACK can only temporarily be effected because continued operation by the engineman would open the time contact and deenergize the electro-pneumatic valve EPV and thus stop the train. In this way the button ACK is protected against improper operation. It might be noted that while the button ACK is operated during the passage of the receiver L over an inert track inductor T, the relays CR and RR are momentarily released and restored and during such operation the whistle valve WV is energized to indicate to the trainman when the relay RR has been restored.

It should of course be understood that when the train passes over a wayside inductor T which has its winding 12 short circuited, in a manner later described, there is insuflicient build-up of tlux through the secondary winding S on the receiver L to cause any release of the relay CR. In other words, when a trackside inductor T is controlled to a clear condition it does not have any stopping etect on the train control apparatus of FIG. 1A.

It should also be understood that any suitable remotely controlled communication selective type system may be employed in place of the Western Electric type telephone selector above described, such, for example, as the selective type system disclosed in the patent to Nelson B. Coley, Patent No. 2,626,314, dated January 20, 1953. It should be understood that the particular type of selector control does not limit the use or operation of the present invention.

More specifically, a wayside track inductor T is located at the entrance at each end of the passing siding PS as shown in FIG. l. As shown, the inductor T at station A has its winding 12 open circuited because contact 20` of relay DS is normally open. The trackside inductor T at the station B at the other end of the passing siding PS is normally in the same condition.

When an eastbound train is to meet a westbound train at this passing siding PS, then the central operator does nothing for the control of these wayside elements or inductors T because each train should stop at this passing siding for meet purposes. The engineman on each train has been so advised by suitable train orders.

Thus, when the eastbound train approaches the passing siding PS, he must actuate the acknowledgment button ACK while his engine is passing the wayside inductor T at station A. Should the engineman of this train fail to thus temporarily acknowledge the presence of the track inductor T, the train is automatically stopped as above described.

A similar operation must take place with regard to the westbound train in passing the track inductor T at station B. It is of course to be understood that one of the trains may take the main track and the other may take the passing siding. The track switches must be appropriately set by the trainman, or they may be spring switches allowing entering movements and adapted to be trailed by the trains as they leave. On the other hand, power operation of the track switches may be provided if so desired.

From the above, it can be seen that when two trains are to meet at the passing siding PS in accordance with train orders issued to them, such trains must appropriately acknowledge their approach to the passing siding PS, or they will be automatically stopped.

Let us assume, however, that an eastbound train is approaching the passing siding, and the central operator desires to allow that train to proceed in accordance with its train orders without meeting any contlicting train at such passing siding. The central oice operator under such conditions transmits a suitable control code over the telephone selector system for selecting station A and effecting a clear control at that station. Such control code transmitted over the system is received by the remote controlled telephone selector 4 at station A and temporarily closes contact 15 at that station. The closure of this contact 15 applies energy from through contact 15, to the winding of relay DS at that station, to The contacts of relay DS immediately pick up so that a stick circuit is closed from (-1-), through resistor 18, back contact 17 of relay IN, front contact 16 of relay DS, winding of relay DS, to This maintains the relay DS picked up closing front contact 20 to complete a shunt circuit on winding 12 of the track inductor T at that station A including ythe Vrelay IN. This condition is maintained in spite of the opening of contact 15.

When the eastbound train, which has no orders to meet another train at the passing siding PS, passes the station A, the train carried receiver L produces some flux through the track inductor T but such ilux does not rise to a maximum value because the winding 12 is short circuited and the self-inductance prevents the magnetic ilux from rising to the maximum value as would occur if the winding 12 were not short circuited. However, there is suicient flux rise in the soft iron laminations of the track inductor T to produce some induced current in the winding 12 and hence in the relay IN. This induced current causes the relay IN to actuate its contact 17 to a picked up position. Such opening of back contact 17 opens the stick circuit of relay DS so that its contacts are released. In this way, any subsequent train receives a stop control at this inductor T at station A unless a subsequent clearing control is received over the remotely controlled telephone selector system.

In this connection, it is noted that the relay IN only momentarily picks up because the induced current is only a momentary current but such operation is suflicient to release the relay DS. However, if desired, the relay IN may have suitable diodes or rectifier units associated with it so as to render such relay responsive to both the negative and positive induced currents due to the passage of the train carried receiver L. If desired, the relay IN may have a diode or rectifier unit associated with it to allow it to respond to only one polarity and then render it slow releasing in its characteristic, While at the same time allowing the current of the opposite polarity to be by-passed. In any event, the function of the relay IN i`s to be momentarily actuated upon the passage of a train carried receiver L.

It should be noted that the track elements or inductors T for eastbound trains are located on one side of the track; whereas, the track inductors T for westbound trains are located on the opposite side of the track. For this reason, no special control has to be transmitted from the central oice 3 as the eastbound train proceeds over the main line passed the track inductor T as station B. In this Way, the eastbound train may proceed from passing siding to passing siding until it reaches one at which it is to meet another train, at which time the operation is as above described. l

In the event that the train does not actually reach the passing siding due to failure of the train, its return y'to some prior siding or the like, the central ofiice operator may desire to cancel a previously transmitted clearing control. For this reason, it is possible for the central office operator to eiect the release of the relay DS by sending a distinctive stop control to the station involved. Such stop control for station A closes contact 19 which connects negative potential to the lower terminal of the resistor 18. This causes a potential drop through Aresistor 18 sufficient that the upper winding of the relay DS is shunted and allows its contacts to release. 'Ihis shunt is applied only temporarily by the contact 19 but 'such time is sulicient for the relay DS to release and open its stick contact 16. In this way, the operator has complete control over the track inductor T.

The operation with regard to station B for a westbound train is exactly the same as that explained in connection with the eastbound train for station4 A with the exception that the clearing control at such station B closes contact 21 momentarily. Likewise, the transmis- 'sion of a stop control over the remote control telephone selector B closes contact 25 momentarily. These remotely controlled contacts have been given distinctive reference characters for stations A and B so as to make clear that each contact is closed only when its distinctive code is received. p

`It should also be understood that the telephone selectorsdisclosed in the above mentioned booklet published by the Western Electric Co. only have contacts which are selectively closed, and for this reason the stop control is shown as providing a shunt to the relay DS; but, if some other selector type system is used in place of the Western Electric selector, then a simple back contact may be employed to open the stick circuit for the relay DS. It will be readily understood that either rarrangement may be readily employed as may be most expedient in practice.

With reference to FIG. 2, the same remote control over a Western telephone selector system is provided for stations A and B; but, in this modication of the present invention it is assumed that there is wayside signaling of the absolute permissive block signaling type such as shown Vin the prior U.S. Patent No. 2,352,986. All of the details of such a signaling system have not been shown for the sake of simplicity in the illustration. However, the signals S4 and SS are illustrated as being of the color light type, and each signal in the patent (see FIG. lA thereof) has what is known as a home distant relay 4HD or SHD respectively associated therewith. These relays are selected through contacts of various track circuits and distant signals in a way to provide the appropriate control all as described in such prior patent. It is suiiicient to know that the track circuit at the left-hand end of the passing siding PS has a track relay T4 connected to it; whereas, the track circuit at the right-hand end of the passing siding has a track relay T5 connected to it. The signal S4 has a distant relay 4HD associated with it which has its selections taken through a front contact of the track relay T4. Whenever the -relay 4HD is deenergized, the signal 4 is at stop. Similarly, the signal S5 has a relay SHD which causes said signal to indicate stop when it is deenergized, and this relay SHD is selected through contacts of relay T5.

In this form of the invention, therefore, the winding 12 of the track inductor T at station A can only be shunted when front contact 31 is closed, that is, when signal S4 is cleared. Similarly, the winding 12 of the ltrack inductor T at station B can be shunted only when the signal SS is cleared as controlled by the relay SHD.

The relay DS2 is shown as having two windings both at station A and at station B. This is merely a way of segregating the pick-up and stick circuits for this relay. The same type of circuits could also be employed in FIG. 1.

In this form of the invention, when the operator sends -a clear control to pick up the relay DSZ to close contact 30 for shunting the winding 12 of the track inductor T at station A, a stick circuit is closed for the relay DS2 including front contact 32 of relay T4 and front contact 33 of relay DSZ. This picking up of the relay DS2 and the closure of its front contact 30 completes a shunt circuit for winding 12 through contact 31 of relay 4HD providingrthe signal S4 is clear. Assuming that the train accepts the clear signal S4 for proceeding past the track inductor T at station A, the release of the track relay T4 when the train has passed the signal S4, opens the stick circuit for relay D52. Thus, the relay DS2 must receive a clear controlfor each eastbound train. In brief,4 this form of the invention differs from that form shown in FIG. l in that the track circuits of the signaling systems are employed for releasing the remotely controlled relays DS2 instead of using relays such as IN of FIG. l. Also, a clear control cannot be etected unless the signaling system shows that the conditions are safe for` the train to pass the entering signal. Otherwise, the operation ,with `respect to FIG. 2 is the same as that 'described in connection with FIG. l. v

Having described two forms of remote control for enforcing train orders by train carried train c ontrol as specic embodiments of the present invention, it is desired to be understood that these forms are selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modilications, adaptations, and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What I claim is:

1. 'In a system for controlling from a central office the movements of passing trains, a stretch of railway track, train stop means carried on each train effective when activated for causing the application of the brakes on that train, wayside means positioned along said stretch of .track for activating said train stop means carried on a train passing thereby, transmitting means at the central oice for selectively transmitting a control signal, receiving means disposed with said wayside means for receiving a transmitted control signal, circuit means con trolled by said receiving means in response to the reception of a control signal for rendering said wayside means ineffective to activate the train stop means carried on a passing train until restored, and means disposed with said wayside means responsive to the passage of that passing train for restoring said circuit means to a normal condition permitting said wayside means to be effective for activating said train stop means carried on any other passing train.

2. A centralized trac control system for supervising from a central ofce the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train effective when activated for causing the application of the brakes on that train, a plurality of wayside means positioned at spaced intervals along said stretch of track, each such wayside means normally operative to effect activation of said train stop means when communicating therewith, receiving means disposed with each said wayside means for receiving a control signal distinctive thereof, transmitting means at the central otnce for selectively transmitting a control signal distinctive of a selected one of said receiving means, circuit means disposed with each wayside means controlled by said receiving means at that location for rendering the associated wayside means ineffective to activate said train stop means upon the passage of the train until restored, and means disposed with each wayside means for responding to the passage of a train to restore said circuit means to a normal inactive condition.

3. A centralized traflc control system for controlling from a central oice the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train effective when actuated for causing the application of brakes on that train, a plurality of wayside elements positioned at spaced intervals along said stretch of track, each such wayside element operative to activate said train stop means when communicating therewith, receiving means disposed with each wayside element effective when distinctively controlled for rendering the associated wayside element ineffective to activate said train stop means, holding means at each wayside element rendered effective in response to the reception of a distinctive control by its associated receiving means for maintaining that receiving means eiective until restored, transmitting means at the central office for selectively transmitting a control distinctive of a selected one of said receiving means, and means located adjacent each wayside element acting in response to the passage of a train for acting on its associated holding means for restoring the associated receiving means to a normal ineffective condition.

4. A centralized traice control system for controlling from a central oice the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train effective when actuated Yfor causing the application of brakes on that train, a ywayside element positioned along said stretch of track, said wayside element operative to activate said train stop means when communicating therewith, receiving means disposed with said wayside element including a stick relay effective when energized for rendering said wayside element ineffective to activate said train stop means, transmitting means at the central oice for selectively transmitting a distinctive control to said receiving means for initially energizing said stick relay, and means located adjacent said wayside element including a relay controlled in response to the passage of a train for deenergizing said stick relay of said receiving means.

5. A centralized traffic control system for controlling from a central office the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train effective when actuated for causing the application of brakes on that train, a plurality of wayside elements positioned at spaced intervals along said stretch of track, each such wayside element operative to activate said train stop means when communicating therewith, receiving means disposed with each wayside element including a stick relay effective when energized for rendering the associated wayside element ineffective to activate said train stop means, transmitting means at the central oice for selectively transmitting a control distinctive of a selected one of said receiving means for energizing its said stick relay, and means located adjacent each wayside element acting in response to the passage of a train for deenergizing the stick relay of the respective receiving means.

6. A centralized traffic control system for controlling from a central office the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train effective to apply the brakes of that train when rendered active, a plurality of wayside track elements located at spaced intervals along said stretch of track normally operative to render a said train stop means active, means at each wayside element for rendering that wayside element inactive upon receiving a control, means at a central oce for transmitting a control distinctive of a selected one of said receiving means, holding means at each wayside element rendered effective in response to the reception of a distinctive control by its associated receiving means for lmaintaining that receiving means effective to hold its wayside track element inactive until such holding means is restored, and relay means located at each wayside element rendered eiective upon the passage of a train past that element for restoring said holding means for that wayside element to in turn restore said receiving means to a normal inactive condition.

7. A centralized traHic control system for controlling from a central oilice the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train effective to apply the brakes of that train when rendered active, a plurality of wayside track elements located at spaced intervals along said stretch of track normally operative to render a said train stop means active when communicating therewith, receiving 4means disposed with each wayside element operable from a normal condition to an operated condition for rendering that wayside element ineffective upon receiving a distinctive clear control, holding means controlled Iby said receiving means for holding said receiving means in an operated condition when it has once been operated to that condition, means at said central Oce for selectively transmitting a distinctive clear and a distinctive stop control distinctive of a selected one of said receiving means, relay means located at each Wayside element rendered effective upon the passage of a train past that element for releasing said holding means and restoring said receiving means to a normal condition, and other means controlled `by said receiving means upon the reception of a distinctive stop control for releasing said holding means and restoring such receiving means to a normal condition.

8.A .centralized traflic control system for controlling yfrom a central ofice the movements of a railway train passing over a stretch of railway track comprising, train stop means carried on the train elective to apply the brakes of that train when rendered active, a plurality of wayside track elements located at spaced intervals along said stretch of ltrack normally operative to render a said train stop means active when communicating therewith, receiving means disposed with each wayside element for rendering that Wayside element inactive upon receiving a distinctive control, said receiving means including means for maintaining it effective until restored, means at said central office for selectively transmitting a control distinctive of a selected one of said receiving means, and relay means located at each wayside element including a track relay rendered effective upon the passage of a train past that element for restoring said receiving means to a normal inactive condition.

9. In combination, train stop means carried on a passing train effective to apply the brakes thereof when rendered active, a plurality of wayside track elements located at spaced intervals along a stretch of railroad track, each such track element normally operative to act on said train stop means to effect the stopping of the passing train but having an inactive condition, a stick relay located adjacent each track element, a pickup circuit for each relay when closed for causing energization of that relay, a stick circuit for each stick relay, means adjacent each wayside element including a winding thereon andan associated relay for opening said stick circuit upon the passage of a train, and remotely controlled"means for selectively closing said pick-up circuit for a particular said track element.

`10. In combination, a stretch of railway track, a plurality of wayside track elements located at spaced intervals along said stretch of track, each such element in Ia normal condition being capable of stopping a train passing thereby but having an inactive condition, remotely controlled -means for rendering said wayside track elements selectively inactive until such remotely controlled means is restored, and means adjacent each wayside track element including a winding on that wayside element connected to a relay responsive to the passage of a train for restoring its respective remotely controlled means to a normal condition for in turn restoring that wayside track element to a normal condition.

11. A centralized trac contr-ol system for a railroad having a plurality of passing sidings each with an entrance comprising train stop means carried on each train for applying the brakes of that train when rendered active, a wayside track element located in advance of the entrance to each passing siding normally conditioned to act on said train stop means to stop a train, remotely controlled means for each wayside track element for rendering that track element in an inactive condition to allow the passage of a train without acting on its trainstop means, and means controlled by a wayside element in response to each passage of a train for rendering the respective wayside track element active for a subsequent train.

References Cited in the le of this patent UNITED STATES PATENTS 1,654,116 Dicke Dec. 27, 1927 1,876,566 Bushnell Sept. 13, 1932 1,930,920 'Bodde Oct. 17, 1933 2,626,314 Coley Ian. 20, 1953 2,761,961 Hughson et al. Sept. 4, 1956 

